In computer networking, exterior gateway protocols may be used to exchange routing and reachability information between autonomous systems (ASes) on the Internet. One example standardized exterior gateway protocol is the Border Gateway Protocol (BGP), often classified as either a path vector protocol or a distance-vector routing protocol. BGP generally makes routing decisions based on paths, network policies, or rule-sets configured by a network administrator, and is involved in making core routing decisions.
In many network configurations, an AS (or other type of routing domain) may learn several paths to a particular destination address or address prefix. For example, many ASes have multiple border routers (BRs or ASBRs, also sometimes referred to as provider edge devices or “PEs”) that may each provide a valid path to the same destination(s). Alternatively or in addition, certain BRs may also individually have multiple valid paths to the same destination(s), such as where a single BR connects to multiple other BRs or has multiple connections to a same adjacent BR. The BGP protocol has typically handled multiple AS egress options by using “best path selection” techniques to choose one (or more) particular egress routes. However, finer grained control and external influence to this egress route selection has yet to be developed.